This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our present studies involve the characterization of seven complexes of a mutant form of the enzyme PEPCK that represent all of the liganded states along the reaction coordinate. We have previously determined these same liganded states for the wild type enzyme that provided the basis for our recent PNAS publication which was also highlighted in Nature Structural and Molecular Biology and the Faculty of 1000. These studies represent a continuation of that previous work. The current structural studies are designed to support our model that states, in contrast to recent studies suggesting the importance of conformational dynamics in transition state stabilization, our current biophysical data is consistent with the role of conformational dynamics in PEPCK catalysis functioning in the stabilization of the reactive catalytic intermediate, a ground state process. In order to support our other biophysical data we need to obtain structural data on the same crystallographic complexes as were previously determined at SSRL for the wild-type enzyme. Clearly the successful completion of these studies will provide a great deal of insight into our fundamental understanding of the role of the dynamic properties of enzymes in catalytic function.